Method and system for enabling audio speed conversion

ABSTRACT

The present invention provides a method and system for processing an audio signal. According to an exemplary method, an audio signal such as a digital voice signal is received and divided into one or more individual unit cycles. An audio speed conversion operation is enabled by repeating or removing one or more of the individual unit cycles. In particular, repeating one or more of the individual unit cycles decreases audio speed, and removing one or more of the individual unit cycles increases audio speed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application under 37 C.F.R. 1.53(b)of copending patent application Ser. No. 10/343,615 filed Feb. 3, 2003,claims benefit under 35 U.S.C. § 365 of International ApplicationPCT/IB01/01161 filed Jun. 29, 2001, which was published in accordancewith PCT Article 21(2) on Feb. 14, 2002 in English, and claims benefitof U.S. provisional application Ser. No. 60/224,115 filed Aug. 9, 2000.

FIELD OF THE INVENTION

The present invention generally relates to audio speed conversion, andmore particularly, to a method and system that enables audio speedconversion such as voice speed conversion.

BACKGROUND OF THE INVENTION

Speed conversion systems can be used to enable multiple speed operation(e.g., fast, slow, etc.) in video and/or audio reproduction systems,such as color television (CTV) systems, video tape recorders (VTRs),digital video/versatile disk (DVD) systems, compact disk (CD) players,hearing aids, telephone answering machines and the like. Conventionalaudio speed converters generally differentiate between a silenceinterval and a sound interval in an audio signal. Deleting the silenceinterval and compressing the sound interval results in an increasedaudio speed. Conversely, expanding the silence and sound intervalsresults in a decreased audio speed. Many conventional audio speedconverters increase or decrease audio speed at a constant rateindependent of the contents. Accordingly, these types of audio speedconverters can not take full advantage of the silence and redundantintervals of an audio signal.

The process of removing or repeating intervals of an audio signal can beproblematic since it often produces undesirable audible “clicks.”Additionally, the pitch of an audio signal should not be changed ortransformed to other frequencies since the human ear tends to be quitesensitive to these changes. Known prior art algorithms such as the“pointer interval control overlap and add” (PICOLA) algorithm addressthese problems by multiplying an audio signal by a window function in anattempt to smooth the output signal and maintain the original pitch.This results in producing synthetic waveforms that were not part of theoriginal audio signal. Moreover, the use of such algorithms typicallyrequires utilization of fast digital signal processors (DSPs), whichtend to be expensive. Accordingly, it is desirable to provide an audiospeed converter which avoids the use of expensive digital signalprocessors (DSPs), and utilizes more cost-effective processing meanssuch as small programmable logic devices (PLDs). The present inventionaddresses these and other problems.

BRIEF SUMMARY OF THE INVENTION

In accordance with an aspect of the invention, a system for processingan audio signal comprises means for receiving the audio signal anddividing the received audio signal into one or more individual unitcycles and means for enabling an audio speed conversion operation by oneof repeating and removing one or more of the individual unit cycles.

In accordance with another aspect of the invention, a method forprocessing an audio signal comprises steps of receiving the audiosignal, dividing the received audio signal into one or more individualunit cycles, and enabling an audio speed conversion operation by one ofrepeating and removing one or more of the individual unit cycles.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an audio speed converter constructed according to principlesof the present invention;

FIG. 2 is a single unit cycle of an exemplary input audio signalaccording to principles of the present invention;

FIG. 3 is a waveform illustrating an exemplary audio signal according toprinciples of the present invention;

FIG. 4 is a waveform illustrating the periodicity of a sound interval ofan exemplary audio signal according to principles of the presentinvention;

FIG. 5 is a series of waveforms illustrating an example of detecting asound interval and a pitch period according to principles of the presentinvention; and

FIG. 6 is a series of waveforms illustrating examples of audio signalcompression and expansion according to principles of the presentinvention.

The exemplifications set out herein illustrate preferred embodiments ofthe invention, and such exemplifications are not to be construed aslimiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

This application discloses a system and a method for processing an audiosignal which provide advantages over conventional techniques. Accordingto an exemplary system and an exemplary method, an audio signal such asa digital voice signal is received and divided into one or moreindividual unit cycles. An audio speed conversion operation is enabledby repeating or removing one or more of the individual unit cycles. Inparticular, repeating one or more of the individual unit cyclesdecreases audio speed, and removing one or more of the individual unitcycles increases audio speed. According to a preferred embodiment, thereceived audio signal is divided into one or more individual unit cyclesin dependence upon a reference value such that an individual unit cyclestarts at a first sample of the received audio signal that is equal toor greater than the reference value and ends at a last sample of thereceived audio signal that is less than the reference value.

The method may also include a step of determining whether each of theone or more individual unit cycles corresponds to a silence interval.This determination may be made in dependence upon an average power valuefor each of the one or more individual unit cycles. According to apreferred embodiment, the average power value for each of the one ormore individual unit cycles is determined in dependence upon an averageamplitude value for each of the one or more individual unit cycles. Themethod may also include a step of detecting one or more pitch periods inthe received audio signal, wherein each of the one or more pitch periodsincludes one or more of the individual unit cycles. This detection maybe in dependence upon the average power value for each of the one ormore individual unit cycles. An audio speed conversion system capable ofperforming the foregoing method is also provided herein.

Referring now to the drawings, and more particularly to FIG. 1, an audiospeed converter 10 constructed according to principles of the presentinvention is shown. In FIG. 1, an audio speed converter 10 includes azero crossing detector 11 which receives an input audio signal. The zerocrossing detector 11 samples the input audio signal and compares thesampled values to a zero reference value. Sampled values that aregreater than or equal to zero reference value correspond to a positiveinput signal, and sampled values less than the zero reference valuecorrespond to a negative input signal. As will be discussed laterherein, the input audio signal is divided into a series of single unitcycle waveforms.

An absolute value calculator 12 receives the sampled values of the inputaudio signal from the zero crossing detector 11, and computes theabsolute value of each sample. An average power value (P) generator 13receives the absolute values computed by the absolute value calculator12, and calculates an average power value (P) for each cycle of theinput audio signal based on the absolute values. In accordance withprinciples of the present invention, it is important to calculate theaverage power value (P) of a single unit cycle waveform, and not of asingle frame that contains a fixed number of samples, as is the casewith many conventional audio speed converters. According to a preferredembodiment, the average power value (P) is calculated on the basis ofthe average amplitude value. That is, the average power value (P) isequal to the sum of the sample values divided by the total number ofsamples in a cycle. In this manner, the average power value (P) iscomputed for each cycle of the input audio signal.

A silence detector 14 receives the average power values (P) from theaverage power value (P) generator 13 and performs a comparison operationto determine whether or not each cycle corresponds to a silenceinterval. In particular, the silence detector 14 compares each averagepower value (P) with a reference threshold value. When one or morecycles corresponding to a silence interval are identified, a silenceredundancy detector 15 may be utilized in certain modes to calculate theduration of the silence intervals and expand or compress the silenceinterval in accordance with principles of the present invention. Furtherdetails regarding the expansion and compression of intervals will beprovided later herein. Alternatively, when one or more cycles notcorresponding to a silence interval are identified, a sound detector andpitch period detector 16 detects a sound interval in the input audiosignal, and further detects the start of different pitch periods. Apitch redundancy detector 17 detects redundancies in pitch periods inaccordance with principles of the present invention. Further detailsregarding the detection of sound intervals and pitch periods will beprovided later herein.

A control circuit 18 controls the general operation of the audio speedconverter 10. For example, the control circuit 18 enables outputs fromthe audio converter 10 to be stored in an internal buffer memory 19 oran external storage device 20 such as a hard disk, a random accessmemory (RAM), an optical disk or other external memory. The controlcircuit 18 also enables outputs from the audio converter 10 to betransferred to an external device 21 such as a speaker or other device,and receives inputs regarding modes of operation. As will be discussedlater herein, the audio speed converter 10 of FIG. 1 has three differentmodes of operation: a fast mode, a slow mode, and a standby mode.

Further details regarding operation of the audio speed converter 10constructed according to principles of the present invention will now beprovided with reference to FIGS. 1 through 6.

As previously indicated, in FIG. 1 the zero crossing detector 11 of theaudio speed converter 10 receives an input audio signal. According to apreferred embodiment, the input audio signal is a 10 bit digital signal.It is contemplated, however, that input signals of other bit lengths maybe accommodated in accordance with principles of the present invention.The zero crossing detector 11 samples the input audio signal andcompares the sampled values to a zero reference value. According to apreferred embodiment, the zero reference value is 512. It iscontemplated, however, that other zero reference values may be utilizedin accordance with principles of the present invention. As previouslyindicated, the input audio signal is divided into a series of singleunit cycle waveforms.

Referring now to FIG. 2, a schematic diagram of a single cycle 30 of anexemplary input audio signal is shown. In FIG. 2, the dots representexemplary points sampled by the zero crossing detector 11 of FIG. 1 andthe numbers (i.e., 1000, 560, 470, 24) represent possible values ofcertain samples (assuming 10 bits of resolution). As previouslyindicated, the zero crossing detector 11 uses a zero reference value of512 in a preferred embodiment, which is one half a maximum value of 1024(assuming 10 bits of resolution). Consequently, sampled values that aregreater than or equal to 512 correspond to a positive input signal, andsampled values less than 512 correspond to a negative input signal. Bycomparing the sampled values with a zero reference value, the inputsignal can be divided into a series of single unit cycle waveforms, suchas the one shown in FIG. 2. According to principles of the presentinvention, a single unit cycle of the input audio signal is measuredfrom the first sample of the positive half-wave (value≧512) to the lastsample of the negative half-wave (value<512). Such a cycle is thesmallest unit of a signal that is eliminated or repeated by the audiospeed converter 10. As will be discussed later herein, the audio speedconverter 10 of FIG. 1 only deletes or repeats complete unit cycles ofthe input audio signal. The advantage of this method is that signaldeletion or insertion always takes place at zero crossing points, thuspreventing any audible clicks in an output audio signal. In this way,the present invention advantageously provides output audio signalscomprised of actual audio information without synthetic waveforms. Inthe conventional “pointer interval control overlap and add” (PICOLA)algorithm, an input audio signal is multiplied by a window functionwhich results in producing synthetic waveforms that were not part of theoriginal audio signal.

Referring back to FIG. 1, the absolute value calculator 12 receives thesampled values of the input audio signal from the zero crossing detector11, and computes the absolute value of each sample. The average powervalue (P) calculator 13 receives the absolute values computed by theabsolute value calculator 12, and calculates an average power value (P)for each cycle of the input audio signal based on the absolute values.In accordance with principles of the present invention, it is importantto calculate the average power value (P) of a single cycle waveform, andnot of a single frame that contains a fixed number of samples, as is thecase with many conventional audio speed converters. According to apreferred embodiment, the average power value (P) is calculated on thebasis of the average amplitude value. That is, the average power value(P) is equal to the sum of the sample values divided by the total numberof samples in a cycle. In this manner, the average power value (P) iscomputed for each cycle of the input audio signal.

The silence detector 14 receives the average power values (P) from theaverage power value (P) generator 13 and performs a comparison operationto determine whether or not each cycle corresponds to a silenceinterval. In particular, the silence detector 14 compares each averagepower value (P) with a reference threshold value P_(SIL), which may beset according to design choice. If P<P_(SIL), the corresponding cycle isidentified as a silence interval, and if P≧P_(SIL), the correspondingcycle is identified as not being a silence interval (i.e., it containsrecognizable sound). In situations where P<P_(SIL), the silenceredundancy detector 15 may be utilized in certain modes to calculate theduration of the silence intervals and expand or compress the silenceinterval in accordance with principles of the present invention. Furtherdetails regarding this operation will now be provided.

Referring to FIG. 3, a schematic diagram of a waveform 40 of anexemplary audio signal is shown. The waveform 40 of FIG. 3 mayapproximate the input audio signal to the audio speed converter 10 ofFIG. 1. In FIG. 3, the audio signal waveform 40 illustrates threedifferent types of intervals: a silence interval, a quasi-soundinterval, and a sound interval. A silence interval mainly containsbackground noise and is of very low amplitude, with a low and constantaverage power. When the audio speed converter 10 of FIG. 1 is in thefast mode, the silence redundancy detector 15 can compress a silenceinterval by removing part of the silence interval. For example, in FIG.3 if the silence interval T_(SIL) is long, then an interval equal toT_(SIL)−T_(TH) can be removed. The threshold time T_(TH) in FIG. 3 is adelay time that must elapse before compression of a silence interval canoccur. In this manner, sounds (e.g., speech) represented by the audiosignal can be better understood by a listener.

Additionally, when the audio speed converter 10 of FIG. 1 is in the slowmode, the silence redundancy detector 15 can expand the silence intervalby a predetermined time interval equal to T_(SIL-REF)−T_(SIL). Theparameter T_(SIL-REF) limits the maximum expansion time of a silenceinterval. Moreover, this parameter causes the expansion of an originallylong silence interval to be less than the expansion of an originallyshorter interval. In this way, words spoken quickly can be betterunderstood by a listener. If a silence interval is long enough so thatthe result of T_(SIL-REF)−T_(SIL) is negative, then expansion may nottake place since there typically is no need to expand an already longsilence interval.

As indicated by the waveform 40 of FIG. 3, a quasi-sound intervalexhibits greater amplitude than a silence interval, and is typicallyrandom in nature having frequent variations. Due to these frequentvariations, a quasi-sound interval tends to exhibit a relatively lowdegree of periodicity (i.e., redundancy). A sound interval exhibits thelargest amplitude of the three types of intervals, and has a periodicstructure. Due to this periodicity, a sound interval exhibits somedegree of redundancy. Quasi-sound intervals and sound intervals both mayrepresent voice information.

Referring to FIG. 4, a schematic diagram of a waveform 50 illustratingthe periodicity of a sound interval of an exemplary audio signal isshown. In particular, the waveform 50 of FIG. 4 illustrates four pitchperiods, T1 through T4. As indicated in FIG. 4, a pitch period isdefined by the periodicity (i.e., redundancy) in a sound interval of anaudio signal. This redundancy in the sound interval can be used toincrease audio speed. For example, in FIG. 4 audio speed can beincreased by removing the second and third pitch periods T2 and T3 fromthe waveform 50. Conversely, repeating the second and third pitchperiods T2 and T3 in the waveform 50 decreases audio speed.

Referring back to FIG. 1, when the silence detector 14 determines thatP≧P_(SIL) for a given cycle, that cycle is transferred to the sounddetector and pitch period detector 16 for further processing. Inparticular, the sound detector and pitch period detector 16 detects asound interval, such as the one shown in the waveform 40 of FIG. 3, andfurther detects the start of pitch periods, such as the ones shown inthe waveform 50 of FIG. 4. Further details regarding this operation willnow be provided.

Referring to FIG. 5, a series of waveforms illustrating an example ofdetecting a sound interval and a pitch period according to principles ofthe present invention are shown. In FIG. 5, a waveform 60 shows anexemplary input audio signal having pitch periods T1 through T4. Eachpitch period includes one or more cycles. For example, in FIG. 5 thepitch period T1 includes cycles Cy2, Cy3 and Cy4. The pitch period T2includes cycles Cy5, Cy6 and Cy7. The pitch period T3 includes cyclesCy8, Cy9 and Cy10. The pitch period T4 includes cycles Cy11, Cy12 andCy13. The number of cycles included in the pitch periods T1 through T4is represented by the values N1 through N4, respectively. A waveform 61illustrates the average amplitude values corresponding to the differentcycles. In particular, cycles Cy1 through Cy13 have average power valuesP1 through P13, respectively. Note that all of the average power valuesP1 through P13 in FIG. 5 are above the silence threshold value P_(SIL),which is shown as a dotted line.

As indicated by the waveform 60, the cycles Cy2, Cy5, Cy8 and Cy11 eachrepresent the start of a given pitch period detected by the sounddetector and pitch period detector 16 of FIG. 1. This detection may beenabled via the average power values. That is, the average power valuesP2, P5, P8 and P11 corresponding to the cycles Cy2, Cy5, Cy8 and Cy11are higher than the average power values of the other cycles.Accordingly, power (e.g., amplitude) value is a useful criterion fordetecting the start of pitch periods. Since certain audio signals suchas voice signals are dynamic in that their power values vary with time,a reference level (i.e., value) used to detect pitch periods should alsovary with time and follow changes in the input audio signal. Therefore,the present invention uses a reference value for detecting pitch periodswherein a reference value for one cycle depends on the average powervalue of a previous cycle. According to a preferred embodiment, thereference value for a given cycle is set equal to the average powervalue of an immediately preceding cycle multiplied by a constant that isbetween 1 and 2. Therefore, assuming for example that the constant is1.5, the power value P2 is compared to 1.5 times the power value P1.Similarly, the power value P3 is compared to 1.5 times the power valueP2, and so on. In this manner, the reference value used to detect pitchperiods varies from cycle to cycle and exactly follows the dynamicchange of an audio signal such as a voice signal. Therefore, accordingto principles of the present invention, if the average amplitude valueof one cycle is greater than or equal to its reference value, then thatcycle is identified as the start of a pitch period and a logic highsignal is generated for output by the sound detector and pitch perioddetector 16. This output signal of the sound detector and pitch perioddetector 16 is represented by a waveform 62 in FIG. 5. The rising edgeof this output signal may be used to set a memory address pointer toindicate the start of a pitch period.

A detected pitch period may be characterized by two parameters: itsduration T and its total number of cycles N. The similarity between twosuccessive pitch waveforms can be determined by comparing theseparameters. In FIG. 1, the pitch redundancy detector 17 calculates adifference in duration between two successive pitch periods (e.g., T1and T2 in FIG. 5) and compares the result to a reference value ΔT_(REF).The pitch redundancy detector 17 then calculates a difference in thenumber of cycles (e.g., N1 and N2 in FIG. 5) between the two successivepitch periods, and compares the result to another reference valueΔN_(REF). According to a preferred embodiment, if the two conditions|T2−T1|≦ΔT_(REF) and |N2−N1|≦ΔN_(REF) are fulfilled, the twocorresponding pitch periods are considered to be identical. The chanceof identifying two identical pitch periods in a quasi-sound interval,such as the one shown in FIG. 3, is relatively low. However, the chanceof identifying two identical pitch periods in a sound interval, such asthe one shown in FIG. 3, is higher. When the audio speed converter 10 ofFIG. 1 is in the fast mode of operation, the second of two identicalperiods is removed from an audio signal. By doing this, the signalredundancy decreases and audio speed increases. Conversely, when theaudio speed converter 10 of FIG. 1 is in the slow mode of operation, thesecond of two identical periods is repeated in an audio signal. By doingthis, the signal redundancy increases and audio speed decreases.

Referring to FIG. 6, a series of waveforms illustrating examples ofaudio signal compression and expansion according to principles of thepresent invention are shown. In FIG. 6, a waveform 70 illustrates asituation where no signal compression or expansion is performed.Accordingly, all four pitch periods having durations T1 through T4,respectively, are included in an audio signal. A waveform 71 illustratesa situation where signal compression is performed. In particular, onlythe pitch periods having durations T1 and T3 are included in an audiosignal, thereby decreasing signal redundancy. The waveform 71 may resultwhen the audio speed converter 10 of FIG. 1 is in the fast mode ofoperation. A waveform 72 illustrates a situation where signal expansionis performed. In particular, the pitch period having duration T2 isrepeated in an audio signal, thereby increasing signal redundancy. Thewaveform 72 may result when the audio speed converter 10 of FIG. 1 is inthe slow mode of operation. When the audio speed converter 10 is in thestandby mode of operation, an input audio signal is simply loopedthrough the audio speed converter 10 without any speed variation. Whenthe audio speed converter 10 is in the fast or slow modes of operation,the number of deleted or repeated cycles is controlled by the controlcircuit 18. Therefore, the control circuit 18 can calculate the audiospeed at any given moment and provide the result to other devices, suchas the internal buffer memory 19, the external storage device 20 and/orthe external device 21.

Certain other attributes of the present invention have been identified.For example, when the audio speed converter 10 is in the fast mode ofoperation, best results are obtained at a speed that is a maximum oftwice the original speed. If the speed is higher, sounds such as speechbecome less understandable to a listener. Nevertheless, higher speedsmay be used in applications such as a fast forward function of a videotape recorder (VTR) where a complete comprehension of the audioinformation is not required. In such cases, it may be necessary toincrease the values of the reference parameters T_(TH), T_(SIL-REF),P_(SIL), ΔT_(REF) and ΔN_(REF). When the audio speed converter 10 is inthe slow mode of operation, best results are obtained at a speed that isnot lower than half the original speed. While the present invention isparticularly suitable for processing voice signals, the principles ofthe present invention may also be applied to the processing of audiosignals in general, including audio signals such as music containingdata other than and/or in addition to voice data.

As described above, the present invention provides several advantagesover conventional audio speed conversion devices. Exemplary features ofthe present invention are as follows:

-   -   Deletion or insertion of parts of an audio signal always occurs        at zero crossing points, thereby eliminating audible clicks.    -   Simple and fast signal processing is enabled since no        multiplication is required at the deletion or insertion points.    -   An input voice signal is divided into variable-length        cycles/frames, wherein each cycle/frame is equal to a variable        number of signal samples depending on the frequency of the input        audio signal.    -   Elimination (i.e., removal) or insertion (i.e., repetition) of        parts of an audio signal only takes place if two successive        periods are found to be identical.    -   Only part of a silence interval is deleted. The expansion of a        silence interval is inversely proportional to its duration.    -   No time or speed limit for the signal processing is imposed.        This results in good quality audio reproduction. Conventional        audio speed converters often eliminate or repeat a section of an        audio signal depending on the overflow or underflow of a buffer        memory. Also, they often have time and speed limits, which have        to be fulfilled. This often results in loosing complete sections        of an audio signal.    -   The resulting output signal, independent of the momentary speed,        contains only parts of the original audio signal. No        synthetically produced parts are included.    -   The resulting audio speed is not constant. The rate of speed        change depends on the parameters T_(TH), T_(SIL-REF), P_(SIL),        ΔT_(REF), ΔN_(REF) and the input signal. In the fast mode, an        input signal that contains more silence intervals and more        identical intervals will result in a faster output signal than        an input signal having the same duration but opposite features.        In the slow mode, the audio speed converter proceeds in a way        that short silence intervals are expanded more than long silence        intervals.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, of adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

1. A system for processing an audio signal, comprising: means forreceiving said audio signal and dividing said received audio signal intoone or more individual unit cycles; means for enabling an audio speedconversion operation by one of repeating and removing one or more ofsaid individual unit cycles; means for detecting one or more pitchperiods in said received audio signal, wherein each of said one or morepitch periods includes one or more of said individual unit cycle; meansfor generating an average power value for each of said one or moreindividual unit cycles; and wherein said detecting means detects saidone or more pitch periods in said received audio signal in dependenceupon said average power value for each of said one or more individualunit cycles.
 2. The system of claim 1, wherein said receiving meansdivides said received audio signal into said one or more individual unitcycles in dependence upon a reference value such that an individual unitcycle starts at a first sample of said received audio signal that isequal to or greater than said reference value and ends at a last sampleof said received audio signal that is less than said reference value. 3.The system of claim 1, wherein repeating one or more of said individualunit cycles decreases audio speed.
 4. The system of claim 1, whereinremoving one or more of said individual unit cycles increases audiospeed.
 5. The system of claim 1, wherein said received audio signal is adigital voice signal.
 6. The system of claim 1, further comprising meansfor determining whether each of said one or more individual unit cyclescorresponds to a silence interval in dependence upon said average powervalue for each of said one or more individual unit cycles.
 7. The systemof claim 1, wherein said generating means generates said average powervalue for each of said one or more individual unit cycles in dependenceupon an average amplitude value for each of said one or more individualunit cycles.
 8. An audio speed conversion system, comprising: a signaldetector for receiving an audio signal and dividing said received audiosignal into one or more individual unit cycles; circuitry for enablingan audio speed conversion operation by one of repeating and removing oneor more of said individual unit cycles; a pitch period detector fordetecting one or more pitch periods in said received audio signal,wherein each of said one or more pitch periods includes one or more ofsaid individual unit cycles; an average power value generator forgenerating an average power value for each of said one or moreindividual unit cycles; and wherein said pitch period detector detectssaid one or more pitch periods in said received audio signal independence upon said average power value for each of said one or moreindividual unit cycles.
 9. The audio speed conversion system of claim 8,wherein said signal detector divides said received audio signal intosaid one or more individual unit cycles in dependence upon a referencevalue such that an individual unit cycle starts at a first sample ofsaid received audio signal that is equal to or greater than saidreference value and ends at a last sample of said received audio signalthat is less than said reference value.
 10. The audio speed conversionsystem of claim 8, wherein repeating one or more of said individual unitcycles decreases audio speed.
 11. The audio speed conversion system ofclaim 8, wherein removing one or more of said individual unit cyclesincreases audio speed.
 12. The audio speed conversion system of claim 8,wherein said received audio signal is a digital voice signal.
 13. Theaudio speed conversion system of claim 8, further comprising a silencedetector for determining whether each of said one or more individualunit cycles corresponds to a silence interval in dependence upon saidaverage power value for each of said one or more individual unit cycles.14. The audio speed conversion system of claim 8, wherein said averagepower value generator generates said average power value for each ofsaid one or more individual unit cycles in dependence upon an averageamplitude value for each of said one or more individual unit cycles. 15.The audio speed conversion system of claim 8, wherein said average powervalue generator generates said average power value for each of said oneor more individual unit cycles in dependence upon an average amplitudevalue for each of said one or more individual unit cycles.
 16. A methodfor processing an audio signal, comprising steps of: receiving saidaudio signal; dividing said received audio signal into one or moreindividual unit cycles; enabling an audio speed conversion operation byone of repeating and removing one or more of said individual unitcycles; detecting one or more pitch periods in said received audiosignal, wherein each of said one or more pitch periods includes one ormore of said individual unit cycles; and wherein said step of detectingone or more pitch periods in said received audio signal is performed independence upon an average power value for each of said one or moreindividual unit cycles.
 17. The method of claim 16, wherein saidreceived audio signal is divided into said one or more individual unitcycles in dependence upon a reference value such that an individual unitcycle starts at a first sample of said received audio signal that isequal to or greater than said reference value and ends at a last sampleof said received audio signal that is less than said reference value.18. The method of claim 16, wherein repeating one or more of saidindividual unit cycles decreases audio speed.
 19. The method of claim16, wherein removing one or more of said individual unit cyclesincreases audio speed.
 20. The method of claim 16, wherein said receivedaudio signal is a digital voice signal.
 21. The method of claim 16,further comprising a step of determining whether each of said one ormore individual unit cycles corresponds to a silence interval.
 22. Themethod of claim 21, wherein the step of determining whether each of saidone or more individual unit cycles corresponds to a silence interval isperformed in dependence upon an average power value for each of said oneor more individual unit cycles.
 23. The method of claim 22, wherein saidaverage power value for each of said one or more individual unit cyclesis determined in dependence upon an average amplitude value for each ofsaid one or more individual unit cycles.
 24. The method of claim 16,wherein said average power value for each of said one or more individualunit cycles is determined in dependence upon an average amplitude valuefor each of said one or more individual unit cycles.